<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		*{
			margin: 0px;
			padding: 0px;
		}
		.box{
			width: 50%;
			height: 50px;
			background: red url() 0 0 no-repeat;
			float: left;
			padding: 5px;
			box-sizing:border-box; 
			/*max-width: 900px;
			min-width: 500px;*/
		}
		.box1{
			width: 50%;
			height: 50px;
			background: blue url() 0 0 no-repeat;
			float: left;
			padding: 5px;
			box-sizing:border-box; 
			/*max-width: 900px;
			min-width: 500px;*/
		}
		@media (min-width: 900px){
			.box{
				background-color: green;
			}
		}
	</style>
</head>
<body>
	<div class="box">
		
	</div>
	<div class="box1">
		
	</div>
</body>
</html>